1. Field of the Invention
The present invention relates to an apparatus for communication with a radio-frequency tag configured to write and read information on and from a radio-frequency tag, for effecting radio communication with the radio-frequency tag, and also relates to the radio-frequency tag, a radio-frequency communication system including the apparatus for communication with a radio-frequency tag and the radio-frequency tag, and a method for radio communication between the apparatus for communication with a radio-frequency tag and the radio-frequency tag.
2. Description of the Related Art
In various fields of communication, there is available a radio-frequency communication device configured to transmit a transmitted signal toward a desired communication object, and to receive a reply signal transmitted from the communication object in response to the transmitted signal received from the radio-frequency communication device, so that radio communication is effected between the radio-frequency communication device and the communication object. As one form of such a radio-frequency communication device, there is known an apparatus for communication with a radio-frequency tag (interrogator) configured to effect radio communication with small-sized radio-frequency tags (transponders) which store predetermined information. The radio-frequency tags and the apparatus for communication with a radio-frequency tag constitute a so-called radio frequency identification system (RFID system) wherein objects to which the radio-frequency tags are affixed can be identified by writing and reading information on and from the desired radio-frequency tags in a non-contact fashion using an electric wave. The radio-frequency communication device of this RFID system is capable of reading out the information from the radio-frequency tags, by radio communication with the radio-frequency tags, even where the radio-frequency tags are soiled or located at invisible places. For this reason, the RFID system is expected to be used in various fields such as management and inspection of commodities.
As one example of the above-described radio-frequency communication system, there is proposed a radio-frequency communication system including a plurality of apparatus for communication with a radio-frequency tag capable of effecting radio communication with desired radio-frequency tags. JP-2001-92885A discloses a behavior data processing system as an example of such a radio-frequency tag communication system. In this behavior data processing system, a plurality of apparatus for communication with a radio-frequency tag connected to each other by a suitable network are configured to effect communication with radio-frequency tags which move with respective moving objects, for processing in a real-time fashion behavior data indicative of behaviors of the moving objects within a building or compound.
However, the prior art radio-frequency communication system requires a network such as a cable network for mutual information communication among the plurality of apparatus for communication with a radio-frequency tag, and tends to be complicated in system construction. The plurality of apparatus for communication with a radio-frequency tag may be arranged to effect mutual radio communication through a wireless network. In this case, a method for mutual radio communication among the apparatus for communication with a radio-frequency tag is different from a method for radio communication of the apparatus for communication with a radio-frequency tag with the radio-frequency tags, so that the radio-frequency communication system requires different communication arrangements. Thus, there has been a need of developing a technique which permits highly reliable communication among a plurality of apparatus for communication with a radio-frequency tag, with a simple arrangement of each apparatus for communication with a radio-frequency tag.